Internal combustion engine systems may operate a series of gas exchange valves in each cylinder of the engine to provide gas flow through the cylinders. One or more intake valves open to allow charge air with or without fuel to enter the cylinder while one or more exhaust valves open to allow combusted matter such as exhaust to exit the cylinder. Intake and exhaust valves may be poppet valves actuated via linear motion provided directly or indirectly by cam lobes attached to a rotating camshaft. The rotating camshaft may be powered by an engine crankshaft. Some engine systems variably operate the intake and exhaust valves to enhance engine performance as engine conditions change. Variable operation of the intake and exhaust valves along with their respective cam lobes and camshafts may be generally referred to as cam actuation systems. Cam actuation systems may involve a variety of schemes such as cam profile switching, variable cam timing, valve deactivation, variable valve timing, and variable valve lift. As such, systems and methods for cam actuation systems may be implemented in engines to achieve more desirable engine performance. Other attempts to address cylinder deactivation and/or variable valve lift include using hydraulic devices. There are attempts to control the valves by means of hydraulic devices in such a way that the valves can be opened only in predetermined steps or not at all.
However, the inventors have recognized potential issues with such systems. As one example, hydraulic devices utilize complex hydraulic circuits designed to deliver high and low pressure hydraulic fluid to operate actuating mechanisms in order to function as desired. Furthermore, hydraulic devices may be used with other valve lift control devices (e.g., a camshaft), which may lead to packaging issues.
In one example, the issues described above may be addressed by a method comprising rotatably actuating an asymmetric camshaft in a first and second directions in order to variably adjust one or more valves of one or more cylinders, wherein actuation to a first position in the second direction deactivates a first cylinder. In this way, individual cylinder valves may be adjusted independently via a common valve lift control device.
As one example, the asymmetric camshaft is actuated to the first position in the second direction in order to deactivate only a single cylinder of a cylinder bank. The camshaft may be further actuated in the second direction to deactivate one or more of the remaining cylinders in response to an engine load decreasing. The deactivated cylinders may be reactivated by rotatably actuating the camshaft in the first direction, where the first direction is opposite the second direction. In this way, the valve lift control device achieves a combination of variable valve lift control and cylinder shutdown in one system by means of a single arrangement. It is possible both for the instantaneous maximum permissible valve lift to be reduced in the case of a low power demand and for individual cylinders to be shut down in succession in the case of an even lower power demand. As a result, fuel consumption is more economical than in a conventional setup.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.